As the term is used herein, direct-wafer-bonding is intended to mean a process whereby two smooth and flat surfaces are brought together, in physical contact, in the absence of an intermediate layer or film, and usually with the application of a uniaxial pressure, such that the two flat surfaces are locally attracted to each other by Van der Walls forces, so that the two flat surfaces stick or bond together. The crystallites in the two flat surfaces of a direct-wafer-bonded interface can fuse together at elevated temperatures due to the surface-energy-induced migration and growth, or the formation of bonds, between the two surface species.
Silicon is a semiconductor of choice for integrated circuits and electronic devices. However, silicon has an indirect bandgap of about 1.1 eV, which makes silicon a relatively inefficient light emitter.
It has been predicted that reducing the physical size of a silicon crystal in all three dimensions, to that of a quantum box or a quantum dot, forces silicon to behave as a direct bandgap material, and therefore become suitable for optical purposes. Moreover, one can tailor the light emission wavelength throughout the visible spectrum by changing the physical dimensions of the silicon quantum dots (Si QDs). For example, see U.S. Pat. Nos. 5,559,822 and 5,703,896, incorporated herein by reference.
One utility of the present invention is to fabricate a double heterostructure (DH) laser diode (LD). A DH LD is described in U.S. Pat. No. 3,309,553, incorporated herein by reference.
The present invention makes use of nano-patterning. The use of bionanomasks as nanometer-scale patterning masks is described in U.S. Pat. No. 4,802,951, incorporated herein by reference.
It is believed that United States patent applications have been filed describing the creation of the nanodot masks, and a technique for tuning the diameter of the nanodots.
DH AllnGaP p-n diodes that are wafer bonded to GaP are typically used for red LEDs (see F. A. Kish et al. Appl. Phys. Lett. 64, 2839, 1994), while DH InGaN p-n diodes are used for green, blue and white LEDs (see S. Nakamura and G. Fasol, The blue laser diode, Springer, Berlin, 1997).
As described in the publication LONG-WAVELENGTH SEMICONDUCTOR LASERS (G. P. Agrawal and N. K. Dutta, AT&T Bell Laboratories Murray Hill, New Jersey, Van Nostrand Reinhold, New York) it has been suggested that semiconductor lasers might be improved if a layer of one semiconductor material were sandwiched between two cladding layers of another semiconductor material that has a relatively wider band gap. Such a device consisting of two dissimilar semiconductors is commonly referred to as a heterostructure laser, in contrast to single-semiconductor devices called homostructure lasers. Heterostructure lasers are further classified as single-heterostructure or double-heterostructure devices, depending on whether the active region, where lasing occurs, is surrounded on one or both sides by a cladding layer of higher band gap.
FIG. 1 provides an example of a prior art double-heterojunction semiconductor laser 10 having typical dimensions as shown, wherein the hatched area is a thin, about 0.2 micrometer thick, active layer 11 of a semiconductor material whose band gap is slightly lower than that of the two surrounding cladding layers 12 and 13.